1. Field of the Invention
The present invention relates generally to apparatus and methods for treating and correcting spinal abnormalities or conditions, stabilizing the position of the spine and vertebrae thereof and fixing or moving the position of bones other than those in the spine. More specifically, the present invention provides an apparatus and system which includes a plurality of links usable together under various circumstances to treat, e.g., different spinal curvature conditions or bone fractures.
2. Description of the Relevant Art
The prior art includes many different apparatus and methods for treating spinal conditions. Known apparatus utilize elongate plate members having several aligned openings or an elongated slot therein for receiving screws or bolts that are affixed to vertebrae. The plate is secured to the screws or bolts and exerts force on the selected vertebra or vertebrae to move same into a desired position or to maintain same in a desired position. The plate also overlies the majority of the lateral bone surface of the vertebrae.
In using such known plate systems, a problem arises when the points on the vertebrae defined by the screws or bolts are not collinear, i.e., they do not lie in a straight line. This creates a problem for the physician because the openings in the plate are collinear and, therefore, the screws do not line up with the plate openings. The physician has several options to compensate for such nonalignment, all of which present additional problems themselves.
The plate can be contoured in the frontal plane to attempt to line the screws up with the plate openings. Due to the thickness and high strength of the plate, this is essentially impossible to do intraoperatively. Another option is to bend the screws or bolts so that they fit in the slots or openings in the plate. This creates an immediate high stress region in the screw or bolt which can cause failure of the same upon cyclical loading or, even worse, can lead to a fracture of the pedicle of the vertebra.
A third option is to place the screws or bolts in a less than optimum position or trajectory in the pedicle of the vertebrae so that they line up with the plate openings. This too can lead to pedicle fractures or cut-out, as well as nerve root injury.
Other known apparatus for treating spinal deformities are disclosed in U.S. Pat. Nos. 5,102,412 and 5,181,917. These apparatus include elongate rod members which have vertebra engaging means secured thereto in an adjustable fashion. The apparatus can be used with bone bolts or screws, or laminar or pedicle hooks. However, the rods are essentially straight which makes utilizing nonlinear points of connection on adjacent vertebrae difficult without the use of specially formed components. In addition, spinal apparatus and systems such as those disclosed in the aforementioned patents include a large number of moving parts and therefore are inherently susceptible to malfunction.
Accordingly, there is a need in the art for a method and apparatus for treating spinal conditions which avoids the problems of the prior art, permits attachment to nonlinear points on adjacent vertebrae, and provides increased bone volume for grafts and fusion.
The prior art includes various apparatus for the treatment of non-spinal conditions, e.g., in long bones and the pelvis. Such conditions include fractures, joint fusions, osteotomies, etc. The prior art apparatus for treating the aforesaid non-spinal conditions do not permit attachment of the bone fixation device to non-linear attachment points on the bone or bones being treated. Accordingly, there is a need in the art for an improved apparatus and method for the treatment of non-spinal conditions.
The present invention provides an apparatus and method for treating spinal conditions by moving a vertebra to a desired position with respect to additional vertebrae or maintaining the vertebra in the desired position.
The apparatus of the present invention includes a plurality of link members that can be secured to adjacent vertebrae in chain-like fashion utilizing pedicle bolts or screws that are not collinear with each other. The link members can be used to subdivide multiple nonlinear pedicle fixation points into units of two adjacent points which two points can be interconnected with a single link member.
The present invention thus facilitates multiple point fixation using two points at a time to overcome the problem in the prior art of nonalignment between plate openings and pedicle screws. The links form a chain and once they are secured to the pedicle screw or bolt with a locking nut, the result is a rigid construct securely affixed to the vertebrae.
The link members are in the form of plates or rods with opposite end portions and a central portion. The opposite end portions each have an aperture therein configured to receive attachment means affixed to the pedicle of adjacent vertebrae. The central portion of each link member is preferably offset from the end portions so that when the link member is attached to adjacent vertebrae portions of the latter are substantially uncovered by the link central portion. However, the present invention also includes links in which the central portion is not offset.
This offset provides increased vertebrae bone volume as compared with prior art apparatus which overlie the vertebra surface, which increased bone volume can be used for bone grafts and fusion. In addition, the present invention permits visualization of bony maturation using plain X-rays since the links do not overlie the graft area.
The links of the present invention can be used with and secured to pedicle screws, bolts, or pedicle or laminar hooks. A combination of hooks and screws or bolts can be used as well depending on the particular application of the invention. For example, a laminar hook can be used on a lamina that is being fused to avoid damaging its associated facet (joint) such as would be caused by a screw or bolt.
The surface of the link member of the present invention is preferably provided adjacent the apertures in the end portions thereof with radial cuts or other interdigitating structure for facilitating and enhancing the locking engagement of the links with a pedicle bolt, screw, hook, or other link(s) at a desired relative position. The bolt or hook has a threaded extension portion that cooperates with a locking nut, and a wedge-shaped washer if needed, to secure an end of the link member to a vertebra.
The wedge-shaped washer compensates for a lack of parallelism in the axial plane between adjacent bolts or screws.
An additional aspect of the present invention is that link members can be used to secure contralateral chains (formed as described above) to each other at their ends, and/or points intermediate their ends, to form a quadrilateral or ladder-shaped construct having increased torsional stability.
A further aspect of the present invention provides a multi-directional attachment assembly which includes a screw portion or member threaded for engagement with a bore formed in a bone, and a bolt portion or member threaded to receive a plate, rod, etc., and a complimentary threaded locking nut. The bolt portion is adjustable with respect to the screw portion and can be positioned in a location that is optimal with regard to receiving and supporting the aforementioned plate, rod, etc. The bolt portion may be angularly positioned relative the screw portion so that the former engages the plate or rod in a desired manner, for example, a perpendicular fashion. The bolt and screw portions preferably include mating hemispherical portions which are joined on a plane that is oblique to the longitudinal axis of both the screw and bolt portions. The multi-directional attachment device may be used with spinal fixation systems to facilitate optimal placement of the screw portion within the vertebra while permitting adjustment of the bolt portion relative thereto for optimal engagement with the plate and/or rod. In addition, the above-described link structures and multi-directional attachment members may be used in the treatment of non-spinal conditions including fractures, joint fusions, osteotomies, etc.